Breast cancer is the most prevalent form of cancer among women. After treatment completion, breast cancer survivors frequently experience residual symptoms including pain, fatigue, sleep dysfunction, anxiety, depression, and fear of recurrence. This wide range of post-treatment symptoms, and possibly concomitant stress-related cytokine responses, may occur in combination (clusters). Effective interventions for this understudied group of cancer survivors are paramount given the size of this affected patient population. The primary goal of this application in response to RFA PA-07-074 for the first 2 submissions, and PA- 07-070 for this 3rd submission is to rigorously evaluate the efficacy of the Mindfulness Based Stress Reduction (MBSR) Breast Cancer (BC) program among breast cancer survivors. Specifically, we aim to determine: (1) the extent to which the MBSR (BC) program improves patient outcomes after treatment completion; (2) the manner (mechanisms) by which the MBSR (BC) program is effective; and (3) if particular subgroups of patients derive the most benefit from the MBSR (BC) program. To achieve these aims, we will conduct a randomized clinical trial of 330 women with Stage 0, I, II, and III breast cancer who have undergone lumpectomy and/or mastectomy, and are within 2 years of completion of treatment with adjuvant radiation and/or chemotherapy. This period corresponds to the critical transition time when formal medical treatment has ceased, yet residual symptoms remain. Patients will be randomly assigned in equal probability to the MBSR (BC) program or a waitlisted usual care regimen that is later offered the MBSR (BC) program. Patient assessments will be made at baseline, 6 weeks, and 12 weeks, and will include measures of psychological symptoms (depression, anxiety, perceived stress), physical symptoms (pain, fatigue, sleep dysfunction), quality of life, biological stress markers (pro-inflammatory immune cytokines, cellular adhesion molecules, lymphocyte subsets) and stress-related hormones (cortisol, catecholamines). The MBSR (BC) program to be evaluated is a clinical program that provides systematic training to promote stress reduction by self-regulating arousal to stress. Our group has modified this program for breast cancer survivors and shown preliminary evidence of its efficacy in reducing symptoms. Going forward, we will formally test whether: (1) the MBSR (BC) program results in greater initial (6 week) and short-term sustained (12 week) improvements in psychological symptoms, physical symptoms, quality of life, and biological stress markers compared to Usual Care; (2) patients in the MBSR (BC) program report greater increases in mindfulness and larger reductions in fear of recurrence which, it turn, reduce psychological and physical symptoms and stress-related hormones, as well as improve quality of life; and (3) the efficacy of the MBSR (BC) program is greatest among patients who present with high anxiety, high perceived stress, low optimism, poor quality of life, and specific symptom profiles (i.e. highly distressed patients).